Gradient system

ABSTRACT

To supply a programmed gradient to a high pressure pump for introduction into a column, a mixer, degasser and accumulator communicates with the high pressure pump to supply fluid thereto, having a volumn no more than 150 times the chamber volume of the high pressure pump. The mixer, degasser and accumulator includes temperature sensors which sense when the mixer, degasser and accumulator has been emptied to a level where it cannot respond to a demand for fluid from said high pressure pump and provides a signal to a low pressure pump which responds by cycling to again fill the mixer, degasser and accumulator. Upon receiving a demand signal, the low pressure pump fills by drawing fluid from a plurality of fluid sources to compose the gradient being used at that time, with the pump slowing during valve opening and closing so as to avoid cavitation.

This application is a division of application Ser. No. 07/535,565, filedJun. 11, 1990, now U.S. Pat. No. 5,158,675, which is a division of U.S.application Ser. No. 07/355,881, filed May 19, 1989, now U.S. Pat. No.4,981,597, which is a file wrapper continuation of U.S. application Ser.No. 07/023,913, filed Mar. 9, 1987, now abandoned, which is a filewrapper continuation-in-part of U.S. application Ser. No. 06/838,332,filed Mar. 10, 1985, now abandoned, and are assigned to the sameassignee as this application.

BACKGROUND OF THE INVENTION

This invention relates to gradient systems for liquid chromatography.

Gradient programmers are known which control the flow of two or moresolvents to a mixer to provide a constant flow rate of influent to achromatographic column from the mixer while varying the proportions ofthe two or more solvents.

In one prior art programmer of this type, two pumps pump differentsolvents into a mixer, which mixes them into a final influent to thechromatographic column. The rate of pumping of the two pumps is variedwith time so that their sum is constant but the proportions of thesolvent supplied by each differ.

This type of prior art gradient former has several disadvantages suchas: (1) when one of the pumps is pumping at a very low rate or when bothare pumping at nearly the same but differing rates, substantialinaccuracies occur caused by pulsations; and (2) in a high pressureliquid chromatograph, the two high pressure pumps increase the cost ofthe system.

In another prior art system, three low pressure pumps directly feed onehigh pressure pump. Such a system is disclosed in U.S. Pat. No.4,311.586. This system has a disadvantage of being expensive.

In still another prior art system, digitally controlled valves arecontrolled in response to a computer command and each supplies a solventto a chromatographic pump from a different reservoir. A system of thistype is disclosed in U.S. Pat. No. 4,128,476 issued Feb. 2, 1982, toJohn V. Rock. This system has a disadvantage of risking overlappingvalve openings and thus imprecise compositions of liquids.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the invention to provide an improvedchromatographic system.

It is a further object of the invention to provide a novel gradientformer.

It is a still further object of the invention to provide a novelgradient elution system which provides a good mixing efficiency both athigh constant flow rates and low constant flow rates of influent into achromatographic column.

It is a still further object of the invention to provide a novelgradient elution system for liquid chromatography in which theproportioning of solvents from one or more sources is independent ofchanges in valve response and viscosity of liquids.

It is a still further object of the invention to provide a novel highpressure gradient elution system in which the programming of the mixtureof solvents forming the influent to the chromatographic column isindependent of the action of the high pressure pump.

It is a still further object of the invention to provide a high pressurechromatographic system which includes a mixer that receives fluid from alow pressure system in sufficient quantities to maintain a reservoir andsupplies the fluid on demand to a high pressure pump.

It is a still further object of the invention to provide a gradientformer in which a mixer reservoir draws mixed solvents at a low pressurein proportions controlled by the gradient programmer when the liquidlevel within it falls below a predetermined level and supplies themixture upon demand to its outlet.

It is a still further object of the invention to provide a noveldegasser for a liquid chromatograph.

It is a still further object of the invention to provide a gradientformer in which a pump draws fluid in a return stroke from one or moresources in controlled proportions and supplies them to a mixer in aforward stroke.

It is a still further object of this invention to provide a gradientformer in which a mixer demands liquid when it drops below a certainlevel and a pump responds by drawing fluid from one or more sources toinsert into the mixer with the speed of the pump being controlled toavoid cavitation taking into account valve opening time.

It is a still further object of the invention to provide a novelcombination mixer, degasser and reservoir for solvents.

It is a still further object of the invention to provide a novel valvecontrol system that monitors the time duration between energization of avalve and its opening and corrects the time for initiating energizationfor changes in this time duration.

It is a still further object of the invention to provide a novelgradient former usable with high pressure pumps of different capacityand design.

It is a still further object of this invention to provide a novel valvesystem for supplying liquids from a plurality of sources of fluids foruse in a liquid chromatograph.

In accordance with the above and further objects of the invention, a lowpressure pump draws fluid from one or more sources of solvent andsupplies the fluid at low pressure to a mixer, with the mixer signallingwhen it is able to receive more fluid. A high pressure pump removesfluid from the mixer to supply it to the liquid chromatograph.

Advantageously, the low pressure pump has multiple speeds and thesources of solvents are connected through valves to the pump. During itsfilling stroke, the pump adjusts its speed to prevent cavitation ofliquid flowing into the low pressure pump, taking into account valveopening time. The speed of the pump during delivery is sufficiently fastto cause mixing when expelled into the mixer. To provide better controlof the composition of liquids, the signals caused by a change ininductance in solenoid coils is detected: (1) when valves are energized;and (2) when opened. Changes in the difference between the time ofenergization and opening of the valves is stored. The timing of the pumpand valve switching are corrected accordingly on the next cycle. Thevalves open to supply solvent from one source only for each time periodthe pump slows to prevent two sources from supplying solvent at onetime. A tree arrangement of valves minimizes the number of valves formultiple solvents and improves precision in composition.

As a feature of this system, the low pressure pump and mixer, duringstart up of the high pressure pump, can supply a selected fluid orselected fluids to the high pressure pump under some pressure insufficient quantities to prime the high pressure pump. For this purpose,the control system that fills the mixer on demand is bypassed and thepump continues to pump fluid to the mixer from which it flows to thepump under pressure of a spring biased check valve which is leaky to airunder normal conditions but creates pressure under continuous pumping toprime the high pressure pump. The inlet check valve for air entering themixer is not spring biased.

As can be understood from the above description, the chromatographicsystem of this invention has several advantages such as: (1) the mixingefficiency of this system is independent of the flow rate of the highpressure pump that is supplied with solvents; (2) it is able to prime anassociated high pressure pump; (3) it is able to mix several solventswith precision even though some of the solvents may be at a low amount;(4) it is an economical approach to high pressure gradient liquidchromatography; (5) it can operate in a stand-by condition automaticallyat low speeds with one solvent; (6) it provides efficient degassing; (7)changes in the time between energization of a valve and its opening istaken into account in switching; and (8) a tree valving system improvesthe precision of mixing to a programmed composition.

SUMMARY OF THE DRAWINGS

The above-noted and other features of the invention will be betterunderstood from the following detailed description when considered withreference to the accompanying drawings in which:

FIG. 1 is a block diagram of a liquid chromatographic systemincorporating the gradient system of this invention;

FIG. 2 is a block diagram of a gradient system which forms a portion ofthe block diagram of FIG. 1;

FIG. 3 is a block diagram of a portion of the gradient system of FIG. 1;

FIG. 4 is a block diagram of a portion of the system of FIG. 3;

FIG. 5 is a schematic circuit diagram of a portion of the block diagramof FIG. 4;

FIG. 6 is a schematic circuit diagram of another portion of theembodiment of FIG. 4;

FIG. 7 is a schematic circuit diagram of a portion of the embodiment ofFIG. 3;

FIG. 8 is a block diagram of a portion of the embodiment of FIG. 3;

FIG. 9 is a schematic circuit diagram of a portion of the embodiment ofFIG. 8;

FIG. 10 is a schematic circuit diagram of another portion of the blockdiagram of FIG. 8;

FIG. 11 is schematic circuit diagram of still another portion of theblock diagram of FIG. 8;

FIG. 12 is a block diagram of another portion of the block diagram ofFIG. 8;

FIG. 13 is a schematic circuit diagram of a portion of the embodiment ofFIG. 12;

FIG. 14 is a schematic circuit diagram of still another portion of theblock diagram of FIG. 12;

FIG. 15 is a schematic circuit diagram of still another portion of theblock diagram of FIG. 12;

FIG. 16 is a schematic circuit diagram of still another portion of theblock diagram of FIG. 8;

FIG. 17 is a block diagram of a portion of the embodiment of FIG. 2;

FIG. 18 is a block diagram of a portion of the embodiment of FIG. 17;

FIG. 19 is a block diagram of another portion of the embodiment of FIG.17; and

FIG. 20 is a schematic circuit diagram of still another portion of theembodiment of FIG. 17;

FIG. 21 is a schematic circuit diagram of still another portion of theembodiment of FIG. 17; and

FIG. 22 is a sectional view of a portion of the embodiment of FIG. 2.

DETAILED DESCRIPTION

In FIG. 1, there is shown a block diagram of chromatographic system 10having a gradient system 12, a high pressure pumping system 14, a highpressure pump control system 16, a chromatographic column and injectorsystem 18 and a detector and collector system 20. The gradient system 12communicates with the high pressure pumping system 14 to supply solventsthereto mixed in proportions in accordance with a gradient program. Thehigh pressure pumping system 14 communicates with the chromatographiccolumn and injector system 18 to supply the influent thereto fordetection and at times collection by the detector and collector system20.

The gradient system 12 is electrically connected to the high pressurepump control system 16, the chromatographic column and injector system18 and the detector and collector system 20 to receive signals therefromfor data management and to apply signals thereto for controlling otherunits.

The high pressure pumping system 14, the high pressure pump controlsystem 16, the chromatographic column and injector system 18 and thedetector and collector system 20 are not part of this invention exceptinsofar as they cooperate with the gradient system 12 to enable highpressure gradients to be delivered to a liquid chromatographic columnwith precision at both low flow rates and high flow rates.

The gradient system 12 includes a low pressure pumping and mixing system24 and a general system controller 22. The general system controller 22contains the the gradient program as well as other control circuits suchas, for example, for injecting samples into the chromatographic columnor providing data acquisition and processing functions in conjunctionwith the detector and collector system 20. The general system controller22 is not part of the invention except insofar as it provides signals tothe low pressure pumping and mixing system 24 which represent thegradient to be pumped.

The low pressure pumping and mixing system 24 mixes together solvents inproportions under the control of the system controller 22 and suppliesthem to the high pressure pumping system 14 at the rate required by thehigh pressure pumping system 14, supplying an efficiently mixed gradientindependently of the flow rate demanded by the high pressure pumpingsystem 14.

In FIG. 2, there is shown a block diagram of the gradient system 12having a system controller 22, a low pressure pumping and mixing system24 and a power supply 30. The power supply 30 and system controller 22are not part of the invention except insofar as they cooperate with thelow pressure pumping and mixing system 24 but the power supply 30supplies power to other units and the system controller 22 providescertain data management and control functions.

In the preferred embodiment, the system controller 22 includes amicroprocessor with a user input/output keyboard and display 52electrically connected to a digital control unit 50 into which the usermay insert information such as flow rate starting time and stopping timethrough the use of a conventional user input/output keyboard.

To provide solvents through conduit 26 to the high pressure pumpingsystem 14 (FIG. 1), the low pressure pumping and mixing system 24includes a plurality of solvent sources shown generally at 44, a pump,valve and motor assembly 42, an analog control circuit 40 and a mixer,degasser and accumulator 46. The solvent sources 44 are conventionalsolvents for liquid chromatography each contained in its own containerwhich communicates by conduits with the pump, valve and motor assembly42.

The analog control circuit 40 is connected to the digital control unit50 to receive signals controlling starting time, time duration andgradient mixtures to be used in a chromatographic run. The analogcontrol circuit 40 is electrically connected to the pump, valve andmotor assembly 42 to control the mixing and the pumping of solvents tothe mixer, degasser and accumulator 46. The mixer, degasser andaccumulator 46 supplies signals to the analog control circuit 40indicating when it is nearly empty and the analog control circuit 40responds by causing the pump, valve and motor assembly 42 to supply apreprogrammed mixture of solvents to the mixer, degasser and accumulator46 from the solvent sources 44.

In FIG. 3, there is shown the analog control circuit 40 electricallyconnected to the pump 62, the mixer, degasser and accumulator 46, avalve assembly 60, the solvent sources 44 and the digital control unit50 to: (1) receive signals from the digital control unit 50, the pump62, the valve assembly 60 and the mixer, degasser and accumulator 46;and (2) in accordance with such received signals control the valveswithin the valve assembly 60 and the pump 62.

To permit selection of solvents to be mixed in the pump 62, the valveassembly 60 includes a tree arrangement of valves communicating with thesolvent sources 44 and the pump 62. The use of a tree in which only oneof several paths can be open at a time to a plurality of solvent sources44 simplifies switching functions since, when one path is open to selecta solvent, all others are inherently closed without the need for thevalves through which a solvent was previously flowing being deactivated.This renders the release time of the valve through which fluid isflowing less critical when a different fluid is to be selected. In thepreferred embodiment, the valves are released when no fluid is beingdelivered by the pump 62 to the mixer, degasser and accumulator 46. Thesolvent is programmed to be removed from the supply vessels for 100percent of the aspirating time of the pump.

In the preferred embodiment, the valve assembly 44 includes two threeport valves, which are a first electrically activated valve 70 and asecond electrically activated valve 72. The solvent sources 44 includesthree solvent sources 74, 76 and 78. The valve 72 has its normallyclosed outlet port communicating with the pump 62, a first normally openinlet port communicating with a normally closed port of the valve 70 anda normally closed inlet port communicating with a source of solvent 74.A normally open inlet port of the valve 70 communicates with a source ofsolvent 76 and a normally closed inlet port of the valve 70 communicateswith a source of solvent 78.

With this arrangement, the second valve 72 is normally in communicationwith the source of solvent 76 but may be switched to put it incommunication with the source of solvent 78 by changing the valve 70.Moreover, both of those sources may be disconnected and the valve 72 maycommunicate instead with the source 74. Any of those sources may beselected or all of them in sequence to communicate with the pump 62 forpumping through a conduit 48 to the mixer, degasser and accumulator 46.

The mixer, degasser and accumulator 46 is sized so that it includes avolume of liquid at least sufficiently large to fill the cylinder of ahigh pressure pump so that the mixxer, degasser and accumulator 46 isable to continuously supply fluid to the high pressure pump irrespectiveof the flow rate being pumped by the high pressure pump. The lowpressure pump 62 is sized to be able to maintain the mixer, degasser andaccumulator full and thus must either operate rapidly or have asufficient size cylinder to be able to fill the mixer, degasser andaccumulator 46 regardless of the rate of withdrawal by the high pressurepump. Its pump stroke must such that it permits adequate time for thevalves 70 and 72 to open to apply solvent to the pump for mixing thereinand pumping to the mixer, degasser and accumulator 46.

To enable the valves 70 and 72 to be more precisely controlled, the pump62 and the mixer, degasser and accumulator 46, the analog controlcircuit 40 includes a valve sensing and control circuit 80, a pumpsensing and control circuit 82 and a mixer sensing circuit 84. The valvesensing and control circuit 80 is electrically connected to the valves70 and 72 to receive signals indicating whether they are energized oropening and supply controlling signals to open or close them.

The valve tree includes valves having relatively small, precision, valveports so as to create a precise gradient. Large ports causeunpredictable changes in flow rates from different solvents whenswitching occurs between two solvents and may create a pressure drop ofsignificance because of their size. To avoid cavitation and uncertaintyin the liquid flowing into the pump, the pump speed is controlled thusreducing the rate of flow of the liquid at times to avoid unpredictablechanges and cavitation. The pump is slowed to a low rate while thevalves are opening, then gradually increased to a medium rate when thevalves through which liquid is flowing are fully open and then slowedgradually for the next valve switching.

When the mixture is in the pump and a delivery stroke has started, thepump speed is increased to a level that aids in mixing when expelledinto the mixer, with an average flow rate equaling the rate of thehigh-pressure pump average flow rate. To cause mixing, at least 50percent of the volume expelled into the mixer in a pump cycle isexpelled in no more than 9 percent of the time period of the cycle.

For this purpose, there are at least three pumping rates, a low rate forvalve switching to change intake liquids, a medium rate for open valvesolvent intake and a high rate for final delivery. In the preferredembodiment, the ratios of switching intake pumping rate to open valveintake pump motor speed pumping rate varies with position of plunger(half sinusoidal stroke speed at constant motor speed) are in the rangesof 1 to 1.5 and 1 to 5 and the range of open valve intake to finaldelivery pump motor speed rate ratios are in the ranges of 1 to 1.5 and1 to 10. The actual flow rates will vary depending on the portion of thestroke but the maximum possible flow rates with such speeds will havethe same ratios as the pump motor speeds described above. Although motorspeeds are directly controlled, the end result is to avoid uncertaintiesand lack of precision in the inflow rates by requiring a low flow, ratewhen the valves are switching, without completely stopping the motor andwithout making such abrupt changes in rate of flow as to causecavitation.

The open valve or intermediate rate of flow is set to provide adequateflow rate without cavitation into the low pressure pump during refill tosupport its designed pumping rate, taking into consideration the lowrates necessary to avoid cavitation during valve switching. The averageof the pumping rate or high rate must be high enough to supply the needsof the high-pressure pump and must at times be high enough to causemixing in the reservoir. The pump rate during valve switching is lowenough to avoid cavitation and unpredictable flow from two solvents butotherwise as high as possible to provide as much contribution to inflowas possible and the intermediate flow rate is set to avoid cavitationwith the highest precision valves possible.

When the high-pressure pump is operating at flow rates below apredetermined rate, which in one embodiment is 5 milliliters, thelow-pressure pump cycle is started when the mixer signals empty and whenthe high-pressure pump is pumping at a rate above the predeterminedrate, the low-pressure pump completes a fill cycle before the emptysignal and starts a pump or delivery cycle on receiving an empty signal.

The pump sensing and control circuit 82 similarly is electricallyconnected to the pump 62 to sense the position of the pump and to changeits speed when appropriate. The mixer sensing circuit 84 is electricallyconnected to: (1) the mixer, degasser and accumulator 46; and (2) thedigital control unit 50. It senses when the mixer, degasser andaccumulator 46 is empty and starts the pump through a cycle by sendingsignals to the control unit 50 which transmits signals to the pumpsensing and control circuit 82 and to the valve sensing and controlcircuit 80 to cause the valves to open and supply solvent to the pump62, which in turn pumps solvents into the mixer, degasser andaccumulator. Supply fluid to the high pressure pump irrespective of theflow rate being pumped by the high pressure pump. The pump 62 is sizedto be able to maintain the mixer, degasser and accumulator full and thusmust either operate rapidly or have a sufficient size cylinder to beable to fill the mixer, degasser and accumulator 46 regardless of therate of withdrawal by the high pressure pump. Its pump stroke must besuch that it permits adequate time for the valves 70 and 72 to open toapply solvent to the pump for mixing therein and pumping to the mixer,degasser and accumulator 46.

The mixer, degasser and accumulator 46 includes an overflow conduitconnected to it through check valves 88. During priming of the highpressure pump, solvent is applied to the mixer, degasser and accumulator46 in sufficient quantities to perform the priming without the requiringof an empty signal from the sensors therein. Under this circumstance,solvent may overflow through the check valve 88A and air may flow intothe mixer, degasser and accumulator through check valve 88B.

The overflow valve 88A is spring biased liquid-tight, but notnecessarily air tight, and closed to at least one-half pound per squareinch to cause pressure to build in the mixer, degasser and accumulatorbut the valve 88B which permits air to enter the mixer, degasser andaccumulator is not spring biased. Moreover, the valve 88A may be airleaky, but in any event air is permitted to freely enter and leave themixer. The pressure in the mixer, degasser and accumulator is increasedduring a priming operation of the high pressure pump by causing asolvent to continuously flow into the mixer, degasser and accumulatorwhile the high pressure pump is operating until the high pressure pumpis primed. The fill signal is inhibited and the flow continues until theoperator terminates the prime signal after the high-pressure pump hasbeen primed.

In FIG. 4, there is shown a block diagram of the mixer sensing circuit84 having a temperature compensation circuit 90, a sensing circuit 92,an unbalance signal and first-derivative circuit 94, a second-derivativecircuit 96, and an output logic circuit 98.

The sensing circuit 92 is electrically connected to the unbalance signaland first-derivative circuit 94 to transmit a signal thereto when themixer, degasser and accumulator 46 (FIGS. 2 and 3) is empty. Theunbalance signal and first-derivative circuit 94, the output logiccircuit 98; the second-derivative circuit 96 and the temperaturecompensation circuit 90 are connected together to permit transmital of atemperature-compensated signal to the output logic circuit 98 andinitiates a pumping and valve command to obtain more solvent in themixer.

In FIG. 5, there is shown a schematic circuit diagram of the sensingcircuit 92, the unbalance signal and first-derivative circuit 94 and thetemperature compensation circuit 90. The sensing circuit 92 senses anempty mixer and applies a signal to the unbalance signal andfirst-derivative circuit 94 which transmits the unbalance signal to theoutput logic circuit 98 (FIG. 4) and transmits its derivative, correctedthrough a connection with the temperature compensation circuit 90 to thesecond-derivative circuit 96 (FIG. 4).

To sense when the mixer, degasser and accumulator 46 (FIG. 3) is empty,the first and second thermistors 100 and 102 are mounted within it withthe thermistor 102 being mounted at a location where it remains belowthe surface of the liquid in the mixer, degasser and accumulator 46 atall times and the thermistor 100 being mounted at a location where whenthe liquid falls below it, it is no longer cooled by the liquid and itwarms, thus changing its resistance.

The capacity of the high pressure pump in the high pressure pumpingsystem 14 and the mixer, degasser and accumulator 46 are selected sothat there always remains within the mixer, degasser and accumulator 46a level of liquid at the end of each stroke of the high pressure pumpthat covers the thermistor 102 to maintain a temperature equal to thatof the temperature of the solvents in the mixer, degasser andaccumulator 46. The thermistor 100 is mounted at the level below whichthe mixer, degasser and accumulator 46 is to be considered empty whenthe influent drops below it. The volume of container and the mixer,degasser and accumulator 46 above that level is equal at least to a fullstroke of the low pressure pump 62.

With this arrangement, the temperature of the thermistor 102 serves as areference. When the temperature of the thermistor 100 changes, itindicates that the solvent has dropped below it permitting it to beaffected by the temperature of the air instead of that of the liquid.The thermistors 100 and 102 are both self-heated thermistors whichmaintain a temperature above that of the higher of the influent andambient air in the preferred embodiment. The level thermistor should beself-heated so that it heats up in air more than the referencethermistor. By heating both of them, local temperature gradients in thesolvent can be accommodated.

To obtain a signal which may indicate that the mixer, degasser andaccumulator 46 is empty, the unbalance signal and first- derivativecircuit 94 includes an output amplifier 106, a bridge circuit 108, and adifferentiator circuit 112. The bridge circuit 108 is electricallyconnected to the thermistors 100 and 102, and to the differentiatorcircuit 112 and generates a signal when the resistance of thethermistory 100 changes. The differentiator circuit providesinstantaneous information and the voltage level provides statusinformation.

To compensate for temperature changes, the temperature compensationcircuit 90 is electrically connected to the differentiating circuit 112and to the output amplifier circuit 106 to correct for temperaturechanges in the bridge 108. With this circuit arrangement, changes in theresistance between the thermistors 100 and 102 cause an unbalance signalto be applied to the output conductors 109 and 111 indicating an emptycondition in the mixer, degasser and accumulator 46 (FIG. 3). Theunbalance signal is differentiated by the differentiator 112 and thederivative is amplified and applied to the second derivative circuit 96(FIG. 4) through conductor 150 to provide a more sensitive indication ofan empty condition for earlier detection.

When the ambient temperature changes, thermistor 168 reduces itsresistance which increases the power of the differentiator by decreasingthe feedback for amplifier 106 through resistors 160 and 164. Thiscompensation is needed because thermistor 100 decreases in resistance onlead 103B and thus, the change in resistance decreases.

To provide a signal to the comparator output logic circuit 98 (FIG. 4)and differentiator 112 indicating that the liquid has dropped below thelevel-measuring thermistor 100, the bridge 108 includes a source 120 ofa positive 12 volts electrically connected through two paths inparallel, which are: (1) the 432 ohm resistor 122 and the referencethermistor 102 to electrical common 124; and (2) the 432 ohm resistor126 through level-measuring thermistor 100 to electrical common 124.

To differentiate the unbalance signal from the bridge 108, thedifferentiator 112 includes the temperature compensation circuit 90 andthe amplifier circuit 106 in the unbalance signal and first derivativecircuit 94 with a 15K (kilohm) resistor 150 and a 3 uf (microfarad)capacitor 153 electrically connected in series between resistor 126 andthe inverting input of the amplifier 106. The output of the operationalamplifier 106 is electrically connected to: (1) the second-derivativecircuit 96 through conductor 150 and (2) the temperature compensationcircuit 90.

To provide temperature compensation, the temperature compensationcircuit 90 includes a first conductor 150 electrically connected to theoutput of the output amplifier 106 and the second input conductor 152connected to the inverting input of the amplifier 106 to form a feedbackpath around the amplifier 106. The compensation circuit includes acapacitor 156, four resistors 158, 160, 162 and 164, a diode 166, athermistor 168 and a source of a positive five volts 170. The thermistor168 is mounted to the panel and has a negative co-efficient ofresistance whereas the thermistors 100 and 102 are mounted within themixer and have negative co-efficients of resistance.

One end of the thermistor 168 is connected to the source 170 of apositive five volts and the other end is connected: (1) to conductor 150through the 732 ohm resistor 162 and the 48.7K (kilohm) resistor 160 inseries in the order named; (2) to conductor 150 through an alternatepath including the resistor 162, the forward resistance of a 1N273 diode166 and the 14.7K resistor 158; (3) to conductor 150 through stillanother path including resistor 162, a 48.7K resistor 164 and the 0.03uf (microfarad) capacitor 156; and (4) to conductor 152 throughresistors 162 and 164.

With this circuit arrangement, the thermistor varies the gain of thefeedback network composed of resistors 160, 162 and 164 and varies thegain of the differentiator 112 to compensate for changes in ambienttemperature and to provide a more reliable indication of the differencebetween the temperatures of the level thermistor 100 when the mixer,degasser and accumulator 46 (FIG. 2) is full and the temperatures of thelevel thermistor 100 in ambient air. The diode 166 and resistor 158decrease the feedback gain corresponding to wet and dry conditions sothat the wet to dry and dry to wet conditions so that the wet to dry anddry to wet transition signals are the same.

In FIG. 6, there is shown a schematic circuit diagram of the secondderivative circuit 96 and the output logic circuit 98. The output logiccircuit 98 receives signals on conductors 109 and 111 indicating anunbalance signal and signals on conductor 150, 205 and 206 from thesecond derivative circuit 96 from which it detects when the liquid levelis sufficiently low to initiate a refill cycle of the low pressure pumpby a sign on conductor 210 to the pump sensing and control circuit 82(FIG. 3). The second derivative circuit 96 is electrically connected toconductor 150 to provide a second derivative for application to theoutput logic circuit 98 to improve the response time.

To form the second derivative of the first derivative signal applied toit by the first derivative circuit 94 on conductor 150, thedifferentiator circuit 96 includes a one microfarad capacitor 190 and a4.7K resistor 192 and amplifier 200. One place of the capacitor 190 iselectrically connected to conductor 150 and its other plate is connectedto one end of the resistor 192. The other end of the resistor 192 iselectrically connected to the summing node 182 through conductor 194 atthe inverting input of amplifier 200.

The second differentiator circuit includes an operational amplifier 200a one uf feedback capacitor 202, a 200K resistor 204 and the source 120of positive 12 volts and the source 170 of positive 5 volts. The outputof the operational amplifier 200 is electrically connected to the logiccircuit through conductor 206 to provide a second derivative signal tothe logic circuit.

Amplifier 200 has its non-inverting terminal electrically connected tothe source 170 of a positive 5 volts and its rails connected betweencommon and a positive 12 volt source 120. The capacitor and resistorfeedback cause the amplifier to produce the second derivative and applyit to the logic circuit, thus indicating a rate of acceleration ofchange in temperature of the level-measuring thermistor 100, indicatingan empty or not empty condition for the mixer, degasser and accumulator46 (FIG. 3).

To provide a signal to the pump sending and control circuit 82 (FIG. 3)from the mixer sending circuit 84 (FIG. 3: (1) a conductor 210electrically connects the mixer sensing circuit 84 (FIGS. 3 and 4) tothe digital control unit 50 (FIG. 2); and (2) the digital control unit50 (FIG. 2) is electrically connected to the mixer-sensing circuit 84.Signals are transmitted on conductor 210 to the digital control unit 50in response to signals indicating an empty condition on conductorw 103Aand 103B (indicated as 103 in FIG. 3).

For this purpose, the logic circuit includes five adjustable thresholdamplifiers 104, 212, 214, 216 and 218, associated with fivepotentiometer circuits 132, 220, 222, 224 and 226, respectively, eachconnected to a NAND gate circuit 228 which, in turn, is connected to atransistor output circuit 230.

The differentiator 112 provides a negative going signal when there is atransition from dry to wet and positive going when wet to dry. When theunbalance and derivative signals are beyond the threshold set in thepotentiometers 140, 220, 222, 224 and 226, the: (1) status circuitprovides a signal; (2) first derivative comparators 212 and 218 providenegative going and positive going signals above the threshold for firstderivative signals; and (3) second derivative and threshold amplifiers216 and 214 providing negative going signals. All the thresholdamplifiers except amplifier 104 sense derivative information andamplifier 104 senses status information.

To cause the threshold amplifier 104 to provide a negative going signalwhen the bridge 108 becomes unbalanced, the inverting terminal ofamplifier 104 is electrically connected: (1) to electrical commonthrough a 1 uf (microfarad) capacitor 128; (2) to the referencethermistor 102 through 1M (megaohm) resistor 134, conductor 111 and the33.2K resistor 138 (FIG. 5) in series in the order named; (3) to thecenter tap 130 of potentiometer 132 through the resistor 134, and a44.2K resistor 136.

In this circuit, the potentiometer 132 has one end of its resistance 140electrically connected to a source 142 of negative 12 volts and itsother end electrically connected to a source 120 of a positive 12 voltsto set a threshold on the inverting terminal of the threshold amplifer104. The non-inverting input terminal of the threshold amplifer 104 iselectrically connected to the ungrounded end of the level-measuringthermistor 100 through the 1M resistor 144.

To cause the threshold amplifier 212 to provide a negative output signalupon receiving a negative going first threshold of an unbalance signal,the non-inverting input terminal of the amplifer 212 is electricallyconnected to conductor 150 to receive the first threshold and theinverting terminal is electrically connected to the center tap of thepotentiometer 220. One end of potentiometer 220 is electricallyconnected to the source 120 of positive 12 volts and the otherelectrically connected to electrical common.

To cause the output of threshold amplifier 216 to provide a negativegoing output signal upon receiving a positive going second derivativepotential, the inverting input input terminal of the threshold amplifier216 is electrically connected to the output of the differentiatingamplifier 200 and its non-inverting input terminal is electricallyconnected to its output through a 200K feedback resistor 225 and to thecenter tap of the potentiometer 224. One end of the potentiometer 224 isconnected to electrical common and its other end is connected to asource 120 of a positive 12 volts.

To cause the derivative amplifier 218 to provide a negative going signalupon receiving a negative going first derivative potential, thenon-inverting input terminal of the derivative amplifier 218 iselectrically connected to conductor 150 to receive the first derivativeof an unbalance signal and its inverting terminal is electricallyconnected to the center tap of the potentiometer 226. One end ofpotentiometer 226 is connected to electrical common and its other end isconnected to a source 120 of a positive 12 volts.

To cause the transistor 230 to provide a positive or negative signal toconductor 210 indicating an empty or not empty mixer, degasser andaccumulator 46, respectively, the transistor 230 is an NPN transistorhaving: (1) its emitter connected to electrical common; (2) itscollector connected to conductor 210 and to a source 170 of a positive 5volts through a 4.7K resistor 132; and (3) its base electricallyconnected to the output of the NAND gate 244 through a 100K resistor234.

To provide a negative going signal when the mixer, degasser andaccumulator 46 becomes empty and a positive going signal when it becomesnot empty, the NAND gate 244 has one input electrically connected to theoutput of NAND gate 240 and its other input electrically connected tothe collector of the NPN transistor 248. The collector of the NPNtransistor 248 is electrically connected to a source 120 through a 10Kresistor 250 and has its emitter connected to electrical common. Thetransistor 230 and the transistor 248 are both 3704 transistors.

To sense an empty condition, one input of the NAND gate 240 iselectrically connected to the output of the threshold amplifier 104 toreceive a positive signal indicating that the bridge 108 is unbalancedand its other input electrically connected to the output of the NANDgate 242, one input of which is electrically connected to the output ofthe threshold amplifier 212 to receive a positive going signal uponreceiving a positive going first derivative potential and its otherinput electrically connected to the output of the threshold amplifier214 to receive a negative going second derivative potential presence ofa negative derivative of voltage on thermistor 100.

To provide a negative output to the base of transistor 248 upon sensinga not empty condition of the mixer, degasser and accumulator 46, theNAND gate 246 has its output electrically connected to the base of theNPN transistor 248 through a 100K resistor 247, one rail electricallyconnected to a source 120 of a positive 12 volts, the other railconnected to electrical common, one input electrically connected to theoutput of the threshold amplifier 216 to detect a negative going signalindicating positive going second derivative of an unbalanced signal fromthe bridge 108; and its other input electrically connected to the outputof the threshold amplifier 218 to receive a negative going transitionindicating a positive derivative of the bridge signal upon the fillingof the mixer, degasser and accumulator 46.

In operation of the mixer sensing circuit 84, the thermistor 102 whichis mounted near the bottom of the mixer, degasser and accumulator 46 ismaintained at a constant heated temperature by the insulatingcharacteristic of the solvent which always covers it whereas thethermistor 100 warms when the fluid drops below it indicating an emptymixer, degasser and accumulator.

The thermistor 100 upon warming unbalances the bridge 108 to generate anegative going signal at the non-inverting input terminal of thethreshold amplifier 104 and if large enough to overcome the positivesignal set in the potentiometer 132 applies a positive going signal tothe NAND gate 240 indicating an empty condition.

In FIG. 7, there is shown a schematic circuit diagram of the valuesensing and control circuit 80 having a valve driven circuit 251, afirst differentiating circuit 252, a second differentiating circuit 254,an output circuit 256 and a blocking circuit 258. The valve drivecircuit 251 is electrically connected to the solenoid winding of thefirst valve and to the conductor transmitting a control signal to openthe valve so as to receive signals indicating the open condition of thevalve and is electrically connected to the first differentiator circuit252 which differentiates the potential across the solenoid winding thatopens the valve.

The second differentiating circuit 254 is electrically connected toreceive the first derivative of the voltage across the relay winding anddifferentiate it to detect the motion of the solenoid plunger andtransmit a signal to the output circuit. The output circuit receives asignal from the blocking circuit to clock signals representing the inputturn-on signal for the valve and passes the second derivative as asignal indicating that the valve is opening.

A second valve is shown at 260 electrically connected to receive apotential from a solenoid winding on conductor 262 and a control turn-onsignal on conductor 264 and transmit the signal 266 indicating that asecond valve is open. There may also be a third control circuitconnected in a similar manner to the second valve control circuit 260 asthe second valve circuit 260 is connected to the first valve circuitshown in detail. The second and third valve circuits will have the samecircuitry (not shown in FIG. 7) and operate in the same manner as thecircuitry for the first valve to be described in greater detailhereinafter.

To generate a signal representing the opening of the first valve, thevalve driver 251 includes an amplifier 270, a PNP transistor 272 and anNPN transistor 274. The amplifier 270 has its input electricallyconnected to a conductor 280 to receive a signal for opening the valveand has its output electrically connected to: (1) the base of the PNP3702 transistor 272 through a 10K resistor 282; (2) to a source of 284of positive 26 volts through the resistor 282 and a 10K resistor 286;(3) to the emitter of the transistor 272 through the resistors 282 and286. The collector of the transistor 272 is electrically connected tothe base of the transistor 274 through a 1.8K resistor 288 and to theemitter of the transistor 274 through the resistor 288 and a 1K resistor290.

To provide valve drive, the transistor 274 has its collectorelectrically connected to: (1) the emitter of the transistor 272 throughthe forward resistance of a 1N5060 diode 292 and a 1K resistor 294 in aseries: and (2) to the valve pouwer source of positive 26 volts throughthe valve solenoid winding 296 for the first valve. Transistor 274 hasits emitter electrically connected to conductor 300 and to a source 302of a negative 26 volts through a 470 ohm resistor 304.

To form a first derivative, the first differentiating circuit 252includes an RC differentiator 306 and an operational amplifier circuit308. The differentiation circuit differentiates the signal from thesolenoid and conducts it to the second differentiating circuit 254.

To differentiate the signal, the differention circuit 252 includes a0.01 uf (microfarad) capacitor 310 and a 4.7K resistor 312 connected inseries between conductor 300 and the inverting terminal of theoperational amplifier 308. One plate of the capacitor 310 and one end ofthe resistor 312 are electrically connected to electrical common throughthe forward resistance of a 1N914 diode 314 and the reverse resistanceof a 1N914 diode 316 to provide rapid recovery from ceraloads.

The operational amplifier 308 is a conventional operational amplifierhaving a negative 12 volt rail 318 and a feedback circuit with a 100Kresistor 320 in parallel with a 0.001 uf capacitor 322. Itsnon-inverting input is grounded and its output is electrically connectedto the second differentiating circuit 254 which is identical to thefirst differentiating circuit 252. The second circuit 254 provides thesecond derivative of the signal to the output circuit 256.

The output circuit 256 includes a 1N914 diode 330, 4050B bufferamplifier 332, and a NAND gate 334. The anode of the diode 330 iselectrically connected to the output of the second differentiatingcircuit 254 to receive an input and the output of the NAND gate 334 iselectrically connected to a conductor 336 to provide a signal indicatingthat the first valve is open. The cathode of the diode 330 iselectrically connected to: (1) electrical common through a 22K resistor338; (2) electrical common through a 0.01 uf capacitor 340 and to theinput of the amplifier 332. The amplifier 332 and the NAND gate 334 havea rail electrically connected to a source 170 of a positive 5 volts andto electrical common. The other input of the NAND gate 334 iselectrically connected to the blocking circuit 258 which applies asignal to block an output during the time interval of the initial valveturn-on signal on conductor 280.

To provide a positive blocking signal against the initial turn-on signalapplied to conductor 380, the blocking circuit 258 generates a positivepulse for application to the NAND gate 336. For that purpose, blockingcircuit 258 is electrically connected to conductor 280 and has itsoutput electrically connected to one of the inputs of the two input NANDgate 336. Its input is electrically connected: (1) to a source 170 of apositive 5 volts through the capacitor 350 and the forward resistance ofa 1N914 diode 354 and to an input of the NAND gate 336 through thecapacitor 350 and an amplifier 356.

In operation, the valve sensing and control circuit receives a valveopening signal from the solenoid when it opens and differentiates it forapplication to a NAND gate. The signal in response to electricalenergization of the valve is blocked by the NAND gate so that only thesignal due to movement of valve plunge is passed to indicate that thevalve is opening. The signals at 336 from the second derivative indicatethe time the valves start to open and the time they are fully opened.This time is used to correct the stored time of opening of valves tocreate the programmed gradient and thus correct for the individual timesrequired by newly installed valves or for drifts in valve switching timefrom the time of the signal to switch. This sensing is accomplishedusing the effect of a change in inductance on d.c. current, resulting ina pulse applied from the coil 296 for the solenoid which operates thevalve. To prevent cavitation, the pump is slowed in speed before thevalves start opening, and slowly increased to a higher speed when thevalves are fully opened.

In FIG. 8, there is shown a block diagram of the pump sensing andcontrol circuit 82 having a pump sensing circuit 360, a sensing circuit362, a pump control circuit 364, a comparator circuit 366 and a motorand motor drive circuit 368. The pump sensing circuit 360 senses thepiston position and piston movement and supply signals to the comparatorcircuit 366 and to the digital control circuit 50 (FIG. 2). The pumpcontrol circuit 364 supplies signals to the comparator circuit 366indicating the desired motion of the pump pistor and the comparatorcircuit 366 supplies the signal to the motor and motor drive circuit 368in response to the signals it receives from the pump sensing circuit 360and from the pump control circuit 364 to control the speed of the motorthrough the motor and motor derive circuit 368. The center position of arefill stroke is sensed by the pump sensing circuit 360 and transmittedthrough conductor 500 to the digital control unit 50.

In FIG. 9, there is shown a schematic circuit diagram of the motorcontrol circuit 364 having a logic circuit 370 and a digital-to-analogconverter 372. The logic circuit applies a code to the digital-to-analogconverter which responds by applying voltages to the comparator circuit366 (FIG. 8) which causes the motor and motor drive circuit 368 to stop,run at low speed, run at medium speed or run at fast speed.

To apply a coded output signal to the digital-to-analog converter 372,the logic circuit 370 includes first and second NAND gates 374 and 376,first and second diodes 382 and 384. The outputs of the first and secondNAND gates 374 and 376 are electrically connected to correspondinginputs of the first and second amplifiers 378 and 380 and tocorresponding cathodes of the first and second diodes 382 and 384.

To control the motor speed, the NAND gate 374 has its inputselectrically connected to input conductor 386 and the NAND gate 376 hasits two inputs electrically connected to conductors 388 to 390respectively. The anodes of the first and second diodes 382 and 384 areelectrically connected to a conductor 392 for application to thedigital-to-analog converter 372 and the outputs of the first and secondamplifiers 378 and 380 are electrically connected to conductors 394 and396 respectively.

A source of 12 volts 398 is electrically connected through a first 10Kresistor 400 to the output of amplifier 378 and through a second 10Kresistor 402 to the output of amplifier 380. The first and second NANDgates 374 and 376 are types 7400, the first and second amplifiers 378and 380 are types 7407 and the first and second diodes 382 and 384 aretypes 1N714.

In controlling the speed of the motor the output signals of the NANDgates 374 and 376 and cause the following results: (1) when the outputof the first NAND gate 374 is a binary zero or low and the output of theNAND gate 376 is a binary zero or low, the motor is stopped; (2) whenthe output of the first NAND gate 374 is a binary one and the output ofthe NAND gate 376 is a binary zero of low, the motor is traveling at aslow speed; (3) when the output of the NAND gate 374 is a binary zeroand the output of the secondary NAND gate 376 is a binary one, the motoris traveling at a medium speed and then the output of the first NANDgate 374 and the second NAND gate 376 are each a binary one, the motoris traveling fast. When both inputs to the NAND gates are positive,their outputs are low and with all other combinations their outputs arehigh.

To supply an analog motor drive circuit and a coded circuit for motorbraking, the digital-to-analog converter 372 includes a first switch410, a second switch 412, a MOSFET switch 414, a first operationalamplifier 416 and a second operational amplifier 418. The outputs of thefirst and second switches 410 and 412 and of the MOSFET 414 are eachelectrically connected to the inverting terminal of the amplifier 416.The output of the amplifier 416 is electrically connected to theinverting terminal of the amplifier 418 through a 22K resistor 422 andthe output of the second derivative amplifier 418 is electricallyconnected through the analog-output conductor 420 to the comparatorcircuit 366 (FIG. 8).

To supply the proper voltages to the analog-output conductor 420, asource 170 of a positive 5 volts is electrically connected to the sourceof the switch 412 through a 50K potentiometer 424 to the source of theswitch 410 through a 250K potentiometer 426, to the gate of MOSFETtransistor 414 through a 47K resistor 428 and to the source of the2N7000 MOSFET 414 through a 50K potentiometer 430.

The amplifiers 416 and 418 have their non-inverting input terminalsconnected to the electrical common and the second operational amplifier418 has a source 120 of a positive 12 volts connected to one of itsrails and a source 142 of a negative 12 volts connected to its negativerail. Each of them has a different one of the 22K resistors 434 and 436connected accross it. The gate of MOSFET switch 414 is connected toconduit 392 to open it, the gate of the switch 410 is electricallyconnected to conductor 394 to open it and the gate of the switch 412 iselectrically connected to conductor 396 to control it so as to applystages of analog-output voltage to amplifiers 416 and 418 and then tothe analog-output conductor 420.

In FIG. 10, there is shown a schematic circuit diagram of a portion ofthe pump sensing circuit 360 which generates an analog voltagerepresenting the speed of the pump for application through conductor 456to the comparator circuit 366. For this purpose, the pump sensingcircuit 360 includes an optical sensor 440, a hysteresis amplifier 442,a frequency-to-voltage converter 444, an analog switch 446 and a NPNtransistor 448. A second portion of the pump sensing circuit whichgenerates a glas position for the mid-refill stroke of the piston isshown in FIG. 11.

The optical sensor 440 is electrically connected through the hysteresisamplifier 448 to the frequency-to-voltage converter 444 to which itapplies pulses indicating the rate of movement of the piston in the pumpfor conversion to an analog-output voltage on conductor 456. Thetransistor 448 receives a signal on conductor 458 indicating a brakingaction and applies a signal through the switch 446 to terminate theoutput of the frequency-to-voltage converter 444 during a brakingaction.

To sense movement of the pump piston, an optical disc illustratedschematically at 441 is mounted to the shaft of the pump motor forrotation therewith through the light beam of the optical sensor 440which senses the indicia and generates electrical pulses therefrom in amanner known in the art. For this purpose, a source 120 of a positive 12volts is electrically connected through the 330 ohm resistor 450 to alight emitting diode within the optical sensor 440 to generate light forapplication through the sensing disc through a light-sensing element.The light sensing element is electrically connected to a source 170 of apositive 5 volts through the 1.2K resistor 452 with the other elementsof the light emitting diode and the light sensor being electricallyconnected to the electrical common of the circuit.

The output conductor 460 of the optical sensor is electrically connectedto the input of the amplifier 442 which serves as a hysteresisamplifier. This amplifier has a 220K feedback resistor 462 and has itsoutput electrically connected to tachometer output conductor 464 and tothe input of the frequency-to-voltage converter 444. The amplifier 442is a type 4050 amplifier.

To generate an analog potential proportional to the frequency of inputsignals, the LM2907 frequency-to-voltage converter 444 has its outputterminals electrically connected to conductor 456 and is biased by asource 120 of a positive 12 volts electrically connected to pins 9 and 8and to pin 11 through a 10K resistor 466 and to pin 12 through theforward resistance of a 1N914 diode 468 the cathode of which is alsoelectrically connected to electrical common. The output of the switch446 is electrically connected to pins 3 and 4 of thefrequency-to-voltage converter 444 and to electrical common through a100K resistor 470. Pin 2 of the frequency-to-voltage converter 444 iselectrically connected to electrical common through the 0.001 capacitor472 and pin 4 is electrically connected to electrical common through the0.05 microfarad capacitor 474.

To decrease the ripple of the analog voltage from conductor 456 when themotor is running slowly, the NPN transistor 448 is electricallyconnected through a 220K resistor 476 to conductor 458 from thecomparator circuit 366. The emitter of the NPN transistor 448 iselectrically connected to electrical common and its collector iselectrically connected to the source 120 of a positive 12 volts througha 10K resistor 478 and to the gate of the switch 446 on pin 6. Pin 8 ofswitch 466 is electrically connected through the 1 MF capacitor 480 toelectrical common. The switch 446 is a type of 4016 analog switch.

With this configuration, the optical sensor 440 senses indicia andgenerates pulses at a frequency proportional to the motor rotation speedfor application to the hysteresis amplifier 442 to the input of thefrequency-to-voltage converter 444. The frequency-to-voltage converter444 converts the frequency to an analog potential proportional to it forapplication to the comparator circuit 366 through conductor 456.

In FIG. 11, there is shown another portion 362 of the pump sensingcircuit 360 having a type 835A optical sensor 490, a 150 ohm resistor492, a 47K resistor 494 and a type 4050 amplifier 496. The opticalsensor 490 detects a position flag 491 connected directly to the pumpshaft to rotate with it and block light between the light emitting andlight sensitive elements at dead center at the end of a delivery strokeof the pump. This element may also be a disc that rotates with the pumpmotor output shaft or an element attached directly to a reciprocatingpump shaft to move linearly in line therewith.

To generate an electrical signal in response to the moving flag, thesource 170 of a positive 5 volts is electrically connected: (1) to theone side of the light emitting element through the resistor 492, theother side being grounded to generate light; and (2) to the lightsensing element through the resistor 494. The other terminal of thelight sensing element is electrically connected to ground to generate asignal indicating the center point of the piston stroke on a conductor498. Conductor 498 is electrically connected to the output conductor 500through the amplifier 496 to provide a signal indicating the centerpoint of a pump stroke. Conductor 500 is electrically connected to thedigital control unit 50.

In FIG. 12, there is shown a block diagram of the comparator circuit 366having an error signal generator 502, an output circuit 504 and a brakeand overspeed circuit 506. The error signal generator 502 iselectrically connected to conductors 456 and 420 to receive the analogsignal representing pump speed from the pump sensing circuit 360 (FIG. 9and FIG. 10) and the signal representing the programmed speed from thepump control circuit 364 (FIG. 8 and FIG. 9) and compares these twosignals. It is electrically connected to the output circuit 504 and thebrake and overspeed circuit to which it applies signals. The outputcircuit 504 is electrically connected to: (1) conductor 501 to receive areset signal from the digital control unit (FIG. 2) to prevent the motorfrom operating during switching the main power to the gradient system;(2) conductor 508 to provide an output signal which controls the motor;and (3). to conductor 516 which provides overcurrent sensing forlimiting the current to the motor.

The brake comparator 520 is overspeed circuit 506 and is electricallyconnected to conductor 456 to receive the analog speed circuit from thepump sensing circuit 360 (FIG. 8 and FIG. 10) and to conductors 394 and396 through which it receives pump speed signals from the pump controlcircuit 364 (FIG. 8 and FIG. 9). Brake and overspeed circuit 506 appliesan output signal on conductor 518 to slow or stop the motor, thus aidingin the changing of speed and stopping of the pump.

In FIG. 13, there is shown a schematic circuit diagram of the errorsignal generator 502 having a speed comparison circuit shown generallyat 510, a damping circuit shown generally at 512 and a summing node 514.

The speed comparison circuit 510 is electrically connected to conductor456 to receive the analog speed signal from the pump sensing circuit 360and to conductor 420 to receive the analog programmed speed signal frompump control circuit 364. It provides an output error signal onconductor 530 to damping circuit 512 which differentiates the signal andapplies the differentiated signal and the original signal to summingnode 514 to which it is connected. The summing node 514 provides the sumof the first differential and the error signal to the output circuit 504(FIG. 12) through a conductor 532.

To compare the actual speed with the commanded speed and generate anerror signal, the speed comparison circuit 510 includes a type LF 353operational amplifier 534 and four 47K resistors 536, 538, 540 and 542respectively. The non-inverting input terminal of the amplifier 534 iselectrically connected to electrical common through the resistor 542 andto conductor 456 through resistor 536. The inverting input terminal ofthe amplifier 534 is electrically connected to conductor 420 throughresistor 538 and to output conductor 530 through the feedback resistor540.

To differentiate the error signal received on conductor 530 from thespeed comparison circuit 510, the damping circuit 512 includes adiffferentiator 550 composed of a first LF 353 amplifier 552 and asecond LF 353 amplifier 554. The series connected resistor 560 andcapacitor 562 are electrically connected at one end to the inputconductor 530 and at the other end to amplifier 552 and the amplifier552 is connected through a 47K resistor 556 to amplifier 554. Theamplifier 554 has its output electrically connected to the summing node514 through a 22K resistor 559.

To differentiate the signal received on conductor 530, thedifferentiator 550 includes a 15K resistor 560 and a 0.1 uf capacitor562 electrically connected in series in the order named betweenconductor 530 and the inverting input terminal of the amplifier 552. Theamplifier 552 has its non-inverting input terminal connected to commonground and has its inverting terminal electrically connected to itsoutput through: (1) a 0.05 uf capacitor 557; and (2) a 250Kpotentiometer 558.

Conductor 530 is also electrically connected through a 22K resistor 564to summing node 514 to apply the attentuated error signal to the summingnode for additional to the differentiated signal.

To invert the output signal from amplifier 552, the amplifier circuit554 has its non-inverting input terminal electrically connected toelectrical common, its rails connected to a source 120 of a positive 12volts and to a source 142 of a negative 12 volts respectively, itsinverting input terminal electrically connected to one end of 22Kresistor 558.

In FIG. 14, there is shown a schematic circuit diagram of the outputcircuit 504 which amplifies the error signal and provides a signal tothe motor drive circuit 368 (FIG. 16). For this purpose, the outputcircuit 504 includes a 2N3704 NPN reset transistor 580, a type LF 353error signal operational amplifier 353 and a 2N4061 motor overcurrentthreshold sensing transistor 584.

To cause amplifier 582 to provide a signal to conductor 508 directlyrelated to the error input signal on conductor 532 but affected by resetsignal from transistor 580 if a reset signal is received on conductor501 to which transistor 580 is connected, conductor 532 is electricallyconnected to the inverting input terminal of the amplifier 582, theemitter of transistor 580 and the collector and base of transistor 584.The signal on conductor 5165 is proportional to the motor current. Toprovide an output error signal on conductor 508 in response to a signalon conductor 532, the amplifier 582 has its inverting input terminalelectrically connected to the emitter of transistor 580 and its outputconnected through a 470K feedback resistor 586 to conductor 532 and tothe collector of transistor 584. Its non-inverting input terminal isconnected to electrical common.

A source 284 of a positive 26 volts provides one supply to amplifier 582and the other supply is electrically connected to: (1) a source 432 of anegative 12 volts through the reverse impedance of a 1N5237B zener diode590; and (2) electrical common through a 4.7K resistor 592. The outputof the amplifier 582 is electrically connected to conductor 508 throughthe forward resistance of a 1N914 diode 594 and to the feedback resistor586.

To provide a reset signal to the amplifier 582, the transistor 580 hasits collector electrically connected to a source 284 of a positive 26volts through a 2.2K resistor 596, its base electrically connected to asource 284 of a positive 26 volts through a 2.2K resistor 596, its baseelectrically connected to the reset conductor 501, to the source 284 ofa positive 26 volts through a 47K resistor 598 and to electrical commonthrough a 100K resistor 600. To provide a current limiting signal fromconductor 516, the PHP transistor 584 has its base and collectorelectrically connected to conductor 532 and its emitter connected toconductor 516.

In FIG. 15, there is shown a schematic circuit diagram of the brake andoverspeed circuit 506 having an overspeed circuit 520 and a brakecontrol circuit 522. The overspeed circuit 520 is electrically connectedto conductor 456 to receive the analog signal representing the speed ofthe pump and is electrically connected to conductors 394 and 396 toreceive a code indicating the programmed speed and it provides an outputsignal on conductor 458 to the comparator 366 (FIG. 8) indicating lowspeed condition of the motor as well as to the brake control circuit522. The brake control circuit 552 receives signals indicating anoverspeed condition from the overspeed circuit 520 and applies thesignal to conductor 518 to reduce speed or stop the motor.

To generate a signal representing overspeed, the overspeed circuit 520includes a 321 derivative amplifier 610, a first 4011 NAND gate 612, asecond 4011 NAND gate 614 and a potentiometer 618. The potentiometer 618establishes a potential which is applied to one input of the derivativeamplifier 610 for comparison with the signal on conductor 456 indicatingspeed.

The output from the derivative amplifier is electrically connected toone input of the NAND gate 612, the other input being electricallyconnected for a logic signal to conductor 394. The output of the NANDgate 612 is electrically connected to conductor 458. NAND gate 614 hasboth of its input terminals electrically connected to conductor 396 andits output electrically connected to the brake circuit 522.

To compare the analog signal indicating speed with a reference level,the potentiometer 610 has one end connected to electrical ground and itsother end connected to a source 170 of a positive 5 volts. Thenon-inverting input is electrically connected to the tap of thepotentiometer 618 which is a 20K potentiometer and to the non-invertinginput of the derivative amplifier 610 through a 180K hysteresis feedbackresistor 620 so as to provide a logical low signal to one of the inputsof the NAND gate 612 if the speed is higher than the value set on thepotentiometer 618 resulting in positive output signal on conductor 458indicating an overspeed condition.

Because the other input of NAND gate 612 is electrically connected toconductor 394, a positive signal is conducted to conductor 458 if thecode is for a medium or zero speed setpoint or when the output ofamplifier 610 is low indicating the motor is running faster than lowspeed. NAND gate 614, because both of its inputs are electricallyconnected to conductor 396, provides a positive signal any time that abinary zero is provided by conductor 396 indicating that it is not atthe high nor the medium speed set point.

To initiate braking action, the brake circuit 522 includes two type 4011NAND gates 622 and 6 24, the 4016 switch 626 and the type 3704 NPNtransistor 628. NAND gate 622 has one of its two inputs electricallyconnected to conductor 458 and its other electrically connected to theoutput of NAND gate 614 and its output electrically connected to both ofthe inputs of NAND gate 624. NAND gate 624 is electrically connected toa source 120 of a positive 12 volts and has its output electricallyconnected to the control gate of the switch 626.

The input of the switch 627 is electrically connected: (1) the source120 of a positive 12 volts through a 10K resistor 630; and (2) to thecollector of the transistor 628 through the resistor 630 and an 820 ohmresistor 632. The output terminal of the switch 627 is electricallyconnected to the base of transistor 628, to its emitter through a 10Kresistor 634. The emitter of the transistor 628 is electricallyconnected to conductor 518 to apply a signal to the motor drive circuitsfor braking action.

With this arrangement, signals are provided to the motor to providedynamic braking upon receiving a signal for slow speed or stop andsignals modulating the drive voltage are applied to maintain the pumpingspeed at the programmed rate.

In FIG. 16, there is shown a schematic circuit diagram of the motor andmotor drive circuit 368 having a motor drive circuit 640, a motor 642,and a brake circuit 644, with the motor drive circuit 640 beingelectrically connected to conductors 516 and 518 to receive signals forslowing the pumping rate.

To receive an error signal for controlling the motor 642, the drivecircuit 640 includes a type 2N3704 NPN transistor 650, a type 2N6292 NPNtransistor 652, a 10K resistor 654 and a 1K resistor 656. To drive bothtransistors 650 and 652 to conduction, conductor 508 with the errorsignal is electrically connected to: (1) the base of transistor 650; (2)the emitter of transistor 650 through the resistor 654; (3) the base oftransistor 652 through the emitter of transistor 654; and (4) to theemitter of transistor 652 through the resistors 654 and 656 in series.

The collectors of transistors 650 and 652 are each electricallyconnected to a source 284 of a positive 26 volts and the emitter of thetransistor 652 is electrically connected to one end of the armature ofmotor 642 to drive this motor, the other end of the armature beingelectrically connected to electrical common through a 1 ohm, 2 wattresistor 608.

To permit dynamic braking, the braking circuit 644 includes a type2N6292 NPN transistor 670, a 1 ohm 2 watt resistor 672, a 1K resistor674, a 0.1 UF capacitor 676 and 1N5060 diode 678. Conductor 518 iselectrically connected to the base of transistor 670 and throughresistor 674 to: (1) conductor 516; (2) the emitter of transistor 670;(3) resistor 608; (4) the anode of diode 678; (5) the first plate ofcapacitor 626; and (6) the second armature of motor 642.

The collector of transistor 644 is electrically connected throughresistor 672 to: (1) the emitter of transistor 652; (2) the cathode ofdiode 678; (3) the second plate of capacitor 626; and (4) the armatureof motor 642. With this arrangement, transistor 670 is driven toconduction by conductors 518 and 516, causing motor 642 to bedynamically braked by dissipating energy through the resistor 672 andotherwise to operate as a motor from the potential across the emitter oftransistor 640 and conductor 516.

In FIG. 17, there is shown a block diagram of a portion of the digitalcontrol unit 50 (FIG. 2) having a flow rate control system 700, a pumpcontroller 702, a chromatographic-run clock system 704, a time of runsystem 706, a gradient control system 708, a prime circuit 709, a primestart and stop circuit 711, and a speed control system 710. The primestart and stop circuit 711 contains the same circuit components andoperator in the same manner as the chromatographic-run clock system 704except it does not receive a reset line and does not contain a primestart and stop circuit of its own.

The flow rate control system 700 and the pump controller 702 are notpart of this invention except insofar as they cooperate with the lowpressure pumping and mixing system 24 (FIG. 1) and any suitabletechnique or circuit for permitting a chromatographer to set the flowrate through the chromatographic column may be employed. In thepreferred embodiment, the flow rate system 700 and pump controller 702are those of the co-pending patent application for chromatographicsystem assigned to the same assignee in the name of Robert W. Allingtonand filed concurrently herewith.

The chromatographic-run clock system 704 provides timing pulses for afixed period of time and then terminates a chromatographic run unlessprogrammed to repeat or manually repeat it. It is electrically connectedto the time of run system 706 which selects segments programmed by timeacross the time period in the time of run system 706 which in turn iselectrically connected to the gradient control system 708 which permitsprogramming of the gradient between two or three solvents within eachtime segment selected and which is connected to the speed control system710 which controls the timing of the low pressure pump 62 and the valvesensing and control circuit 80 to provide continuous eluent to themixer, degasser and accumulator 46 (FIG. 2).

To provide basic timing for a continuous chromatographic run, thechromatographic-run system includes a start switch 712, a flip flop 714,a stop switch 716, a clock pulse generator 718, a AND gate 720, and anOR gate 722. The start switch 712 is electrically connected to the flipflop 714, the set output of which is connected to one of the two inputsto the AND gate 720, the other input being electrically connected to theouput of the pulse generator 718. The stop switch 716 is electricallyconnected to one of the two inputs of the OR gate 722, the other inputbeing electrically connected to the time of run system 706 whichtransmits the pulse at a time set within the time of run system 706.

To control timing of a chromatographic run, the output of the OR gate722 is electrically connected to the reset input of the flip flop 714and the output of the AND gate 720 to the clock pulse input of the timeof run system 706 so that, upon pressing the start switch 712, the flipflop 714 is set, opening the AND gate 720 to clock pulses to begintiming and controlling a chromatographic run within the time of runsystem 706. The run continues until the end of the preset time period oruntil the stop switch 716 is closed, either of which cause the OR gate722 to reset the flip flop 714 to terminate clock pulses and reset thetime of run system 706.

The time of run system 706 periodically selects a segment of thegradient control system 708 which has been pre-programmed to supply afixed mixture of solvents to the pump at times controlled by the speedcontrol system 710 which is actuated by a demand signal on conductor 210from the mixer sensing circuit 84 (FIG. 3).

To prime the pumps, the prime circuit 709 is started by depressing a keyon the keyboard and continuously sends a code which causes solvents toflow (FIG. 3) and a signal to cause pump 62 to pump. The pump and switch703 select valves 70 04 72 at each pump cycle to receive a turn-onsignal. The low pressure pump thus continuously pumps until turned offand solvents A, B or C are pumped to flow into the mixer, degasser andaccumulator 46, clearing the liner of air and causing it to overflowuntil the high pressure pump has been primed and begins pumping. In FIG.18, there is shown a schematic circuit diagram of several stages of thetime of run system 706 and several stages of the gradient control system708. The system as shown generally at 706 receives reset signals onconductor 724 from the reset output terminal of the flip flop 714 countsignals on conductor 726 from the output of the AND gate 720 (FIG. 17)and applies an end of chromatographic run signal from the last stageselected for the chromatographic run through a conductor 728. Thissignal is applied through the OR gate 722 (FIG. 17) to the flip flop 714(FIG. 17), terminating the run and resetting the time of run system 706.

The time of run system 706 includes a plurality of output conductorsthree of which are shown at 728A, 728B and 728C for illustrativepurposes only although many more would normally be included. The outputconductors 728A-728C are generally connected to units within thegradient control system 708 although 728C is shown connected throughconductor 728 through the OR gate 722 (FIG. 17) to reset the flip flop714 (FIG. 16). Any output may be selected for this purpose and controlsthe overall time of running of a chromatographic run.

To select individual segments of gradients, the gradient control system708 includes a plurality of gradient segment circuits two of which areshown at 740A and 740B electrically connected to conductor 728A and 728Brespectively for activation by the time of run system 706 at periodic,programmed intervals.

The gradient segment circuits each have a plurality of outputs which areprogrammed to be sequentially energized shown for example as 730A-738Afor the gradient segment circuit 740A and 730B-738B for the gradientsegment circuit 740B. There may be any number of gradient segmentcircuits even though even only two are shown for illustrative purposesand each may have any number of outputs such as those shown at 730A-738Aso that the time of run system 706 selects at programmed intervalsdifferent gradient segment circuits which in turn sequence through aplurality of outputs in a programmed sequence.

To select certain ones of the outputs 728A, 728B and 728C or as manyothers as are desired, the time of run system 706 includes a counter 742having a plurality of sequentially energized outputs, five of which areshown at 744, 746, 748, 750, and 752, for illustration although theremay be any number of units. The time of run system 706 also includes aplurality of flip flops three of which are illustrated at 754A, 754B and754C and a plurality of switching banks three of which are illustratedat 756A, 756B and 756C to correspond with gradient segment circuits andflip flops. In all of these cases there may be any number of unitsalthough three have been chosen for illustrative purposes.

Each of the switch banks 74A-74C (74C is shown in partial form) has aplurality of contacts each electrically connected to a different one ofthe outputs 744-752 of the counter 742 indicated by corresponding onesof the letters A, B, and C, so that the first bank has contacts744A-752A and the second bank 744B-752B and so on. Each of the banksalso has a corresponding switch arm or aperture 756A-756C.

The switch arms 756A-756C are each electrically connected to a differentset terminal of a corresponding one of the flip flops 754A-754C and tothe reset input terminal of the prior one of the flip flops so thatswitch arm 756B is connected to the reset input terminal of 754A. Withthis arrangement, the switch arms 756A-756C may be set at any placealong the switching bank to cause its corresponding flip flop to be set.It thus selects a gradient segment circuit at a programmed time alongthe sequence of the counter 742 and together with the other switch banksforms a sequence by which the flip flops are set and reset. The switcharm for such banks sets a flip flops and resets the prior flip flop sothat at programmed times output signals are applied to correspondingones of the conductors 728A-728C in sequence.

In FIG. 19, there is shown a schematic circuit diagram of one of thegradient segment circuits 740 having a pulse generator 760A, an AND gate762A, a flip flop 764A and a time of run and segment selector 766A. Thethree input AND gate 762A has one of its three inputs electricallyconnected to the output of the pulse generator 760A to receive pulses ata frequency higher than that provided by the pulse generator 718 (FIG.16), a second of its three inputs electrically connected to conductor728A from the corresponding output of the time of run system 706 (FIG.16) and the third of its outputs electrically connected to the setoutput of the flip flop 764A.

The set input of the flip flop 764A is electrically connected throughconductor 768 to the digital output of the mixer sensing circuit 84(FIG. 3) to sense an empty condition of mixer, degasser and accumulator46 (FIG. 3) and set the flip flop 764 in accordance therewith. Theoutput of the AND gate 762A is electrically connected to the time of runsegment selector 766 so that when a demand signal is received, theparticular one of the gradient segment circuits (in this case 740A)which is receiving a signal from the time of run system 706 receivescount pulses in sequence through conductors 760A-738A.

The reset input terminal of the flip flop 764A is electrically connectedto the last stage of the time of run segment selector 766A to receive apulse resetting the flip flop 764A so as to terminate pulses to the timeof run segment selector 766A and to reset a counter therein throughconductor 768A.

The time of run and segment selector 766A is a circuit unit identical tothe time of run system 706 programmed to provide a series of differentsignals the first one corresponding to the time of high speed pumping ofthe pump, the second to a time of low speed corresponding to when fluidfrom the first mixing valve is introduced, the next one being a time ofhigh speed code, the following one being a time of low speed to receivestill another fluid and the final one being a time of high speedresulting in a return forward pumping stroke to inject the two insertedfluids into the mixer.

After a forward stroke, the pump waits for another demand signal atwhich time it will go through another cycle filling itself with theproportion of liquids as controlled by the programmed selection of aparticular gradient segment circuit, the proportion of each fluid beingcontrolled by the programmed time of slow speed and valve opening.

In FIG. 20, there is shown a schematic circuit diagram of the speedcontrol system 710 showing two stages, one for the output conductors 730and the other for the output conductors 732, each stage having acorresponding one of the OR gates 770-772 and there being many outputsas there are stages in each of the: (1) gradient segment circuits suchas 740A (FIG. 17); (2) gradient control system 708 (FIG. 16); and (3)programmable switch banks 780 and 782.

Each OR gate has a number of inputs corresponding to each of thegradient segment circuits with 730A and 730B being shown forillustration connected to OR gate 770 and with 732A and 732B shown forillustration connected to the OR gate 772. However, any number of inputsmay be connected to one OR gate or an OR gate tree, if necessary, comingfrom a corresponding one of the gradient segment circuits such as 740Aand 740B (FIG. 17).

The outputs of each of the OR gates such as 770 and 772 are electricallyconnected to a plurality of switch armatures in its corresponding one ofthe switching banks such as 780 and 782 respectively. Each of themincludes four switches such as will be described in connection with thebank 780.

As illustrated with the bank 780, the output from the OR gate 770 iselectrically connected to each of four switch armatures 790, 792, 794,and 796, each of which may be connected to a different one of thecontacts 798, 800, 802, and 804, to provide a coded output signal underthe control of the closed switches. The coded output signal indicates tothe analog circuit the time of high speed travel, slow speed travel andvalve opening and return stroke for filling the mixer, degasser andaccumulator 46.

As described in connection with bank 782, a decoder 783 receives signalsand generates signals to open valves and changes motor speed with presetdelays and as in delay lines 785 and 787.

The time measured between time of energization of a valve and time ofopening is recorded and the code for delay time set accordingly in thedelays to increase motor speed only after the valve is open.

In FIG. 21, there is shown a prime circuit 709 having a prime startbutton on the keyboard, and AND gate 812, a switch bank 814 and a pulsegenerator 816. The prime start button 810 applies a pulse to the ANDgate 812 in the same manner as the start button 712, which is to set aflip flop connected to its output. The start button 712 similarlyapplies an output such as that from flip flop 714 and to the AND gate812, but such signal is inverted by an inverter 818 so that before thestart button 712 is depressed to start a chromatographic run, a positivesignal is applied to gate 812 so that when the prime start 810 isdepressed and before the start button 712 (FIG. 17) is depressed, pulsesfrom the pulse generator 816 are applied to the input of the AND gate812 and result in an output signal to the switching bank 814.

The switching bank 814 is set in the same manner as the switching banks780 and 782 (FIG. 20) but to a code to cause valves 70 and 72 to open,the pump 62 to operate and the pump in the high pressure pumping system14 to operate until the start button 712 is depressed for the start of achromatographic run. The chromatographic run is not started by theoperator until solvent A is flowing through the system showing that thepumps have been primed and the column is ready to receive a sample bybeing stabilized with solvent A flowing through it at a stable pressureand constant preset flow rate.

While a proposed hardware circuit has been shown as part of the digitalcontrol unit 50, in the preferred embodiment the unit is partly softwareand partly hardware. An Intel P803AH computer is programmed with a TexasInstruments keypad and appropriate software to generate the digitalsignals controlling the valve and the low pressure pump. The softwareprogram relevant to these functions is summarized below and then givenin full and contains a program to perform the same functions as shown inthe proposed hardware schematics.

The program waits in the RUN-MOD procedure line 1187 until the mixer isempty. If it is empty, the program goes to line 1260. Here thesubroutine Fill is called to fill the pump. Next, subroutine pump iscalled to empty the pump into the mixing chamber. If the HPLC flow rateis less than approximately 5 ml/min., the unit waits until the chamberis empty, then fills the pump and pumps into the chamber, at flow ratesgreater than 5 ml/min. the pump is immediately refilled after the pumpstroke. This eliminates delay from the time the mixer signal arrives,and when the pump delivers the fluid.

In FILL, the program continually reads the angular location of the motorto determine if it is time to change motor speeds or activate one of thesolenoid valves. Once a valve has been activated, the program alsodetects the valve switching signal. When the switching is detected, thedelay is calculated as a function of motor displacement. This value isthe amount of correction used when determining the switching point ofthe valve during the next pump stroke.

The program then goes to PUMP which monitors the unit during fluiddelivery.

    ______________________________________                                        1151 2     FILL: PROCEDURE                                                    1152 2      DECLARE LOCATION WORD;                                            1153 2      DECLARE (V1, V2, V3, V4) BIT;                                     1154 2      V1, V2=0;                                                         1155 2      V3, V4=1;                                                         1156 3      IF SWITCH 2 = 0 THEN DO;                                          1158 3         VALVE 1, VALVE 2 = 0;                                          1159 3         VALL TIME (100);                                               1160 3         END;                                                           1161 3      ELSE IF SWITCH 1 = 0 THEN DO;                                     1163 3         VALVE 1 = 0;                                                   1164 3         CALL TIME (100);                                               1165 3         END;                                                           1166 2      IF SWITCH 1 ) 200 THEN CALL FAST;                                 1168 2      ELSE CALL SLOW;                                                   1169 2      CALL TIME (OFF);                                                  1170 2      LOCATION = TACH;                                                  1171 3      DO WHILE LOCATION (SLOW 1);                                       1172 3         LOCATION = TACH;                                               1173 3         END;                                                           1174 2      CALL SLOW;                                                        1175 2     LOOP: LOCATION = TACH;                                             1176 3      IF (LOCATION ) SWITCH 1) AND V3                                               THEN DO;                                                          1178 3         VALVE 1 = 0;                                                   1179 3         V1 = 1;                                                        1180 3         V3 = 0;                                                        1181 3         END;                                                           1182 3      IF (LOCATION ) SWITCH 2) AND V4                                               THEN DO;                                                          1184 3         VALVE 2 = 0;                                                   1185 3         V2 = 1;                                                        1186 3         V4 - 0;                                                        1187 3         END;                                                           1188 3      IF V1 AND (NOT V CHECK 1) THEN DO;                                1190 3         V1 = 0;                                                        1191 3         ERR 1 = LOCATION - SWITCH 1;                                   1192 3         END;                                                           1193 3      IF V2 AND (NOT V CHECK 2) THEN DO;                                1195 3         V2 = 0;                                                        1196 3         ERR 2 = LOCATION - SWITCH 2;                                   1197 3         END;                                                           1198 2      IF (LOCATION) SWITCH 1 + 15) AND                                           (LOCATION (SLOW 2) THEN                                                       CALL FAST;                                                           1190 2      IF (LOCATION SLOW 2) AND (LOCATION ((                                      SWITCH 2 + 15)) THEN CALL SLOW;                                      1193 2      IF (LOCATION) SWITCH 2 + 15) THEN CALL                                     FAST;                                                                1194 3      IF LOCATION ) = 2183 THEN DO;                                     1196 3         CALL FAST;                                                     1197 3         VALVE 1, VALVE 2 =  1;                                         1108 3         RETURN;                                                        1109 3         END;                                                           1110 3      IF ((CHAMBER AND 20H) ( ) 20H) THEN DO;                           1112 3         P15 = 1;                                                       1113 3         SECONDS = 0;                                                   1114 3         TENTH SEC = 0;                                                 1115 3         I = 0;                                                         1116 3         HFLAG = 0;                                                     1117 3         LED = 14H;                                                     1118 3         TSTART, TEND = 0;                                              1119 3         ACON, AP = SEGMENT (0).SA;                                     1120 3         BCON, BF = SEGMENT (0).SB;                                     1121 3         OPERATE = OAAH;                                                1122 3         CALL CHECKMEM;                                                 1123 3         END;                                                           1124 3      IF MSG THEN DO;                                                   1126 3         CALL MOVCXO(.(`B 98`, CR),750,5);                              1127 3         MSG = 0;                                                       1128 3         SBUF = TBUFFER(0) OR 80H;                                      1129 3         RBUFFPTR = 0;                                                  1130 3         END;                                                           1131 2      GOTO LOOP;                                                        1132 1     END FILL;                                                          1133 2     PUMP: PROCEDURE;                                                   1134 2      DECLARE ADUMMY WORD;                                              1135 2      DECLARE RFLAG BIT;                                                /* GO FASTER DURING DISCHARGE */                                              1136 2      P13,P35 = 0;                                                      1137 2      PDUMMY = 0;                                                       1138 2      CALL CALC;                                                        1139 3      DO WHILE PDUMMY (4150;                                            1140 4         IF ((CHAMBER AND 20H) ( ) 20H)                                                THEN DO                                                        1142 4           P15 = 1;                                                     1143 4           SECONDS = 0;                                                 1144 4           TENTHSEC = 0;                                                1145 4           I = 0;                                                       1146 4           HFLAG = 0;                                                   1147 4           LED = 14H;                                                   1148 4           OPERATE = 0AAH;                                              1149 4           TSTART, TEND = 0;                                            1150 4           ACON, AF = SEGMENT (0).SA;                                   1151 4           BCON, BF = SEGMENT (0).SB;                                   1152 4           CALL CHECKMEM;                                               1153 4           END;                                                         1154 3         PDUMMY = TACH;                                                 1155 4         IF MSG THEN DO;                                                1157 4             CALL MOVCX0(.(`B98`,CR),750,5);                            1158 4           MSG = 0;                                                     1159 4           SBUF = TBUFFER(0) OR 80H;                                    1160 4           RBUFFPTR = 0;                                                1161 4           END;                                                         1162 3         END;                                                           1163 2      CALL SLOW;                                                        1164 3      DO WHILE NOT TDC;                                                 1165 3         END;                                                           1166 2      CALL RESET.sub.-- TACH;                                           1167 2      P13,P35 = 1;                                                      1168 2      CALL TIME (OFFH);                                                 1169 1     END PUMP                                                           1170 2     RUN MOD: PROCEDURE;                                                1171 2      DECLARE (DUM,J) BYTE;                                             1172 2      DECLARE CATCH BIT;                                                1173 2      FILLTIME = 40;                                                    1174 2      XFILL = 0;                                                        1175 2      LED = 14H:                                                        1176 2      IF HFLAG THEN LED = 94H                                           /* FOR POWERUP */                                                             1178 2      CALL CHECKMEM;                                                    1179 2      I=0;                                                              1180 2      TSTART, TEND = 0'                                                 1181 2      ACON,AF=SEGMENT (0).SA;                                           1182 2      BCON,BF-SEGMENT (0).SB;                                           1183 3      DO WHILE NOT TDC;                                                 1184 3         END;                                                           1185 2      P16 = 1;                                                          1186 2      CALL RESET.sub.-- TACH;                                           1187 3     TAG1: DO WHILE ((CHAMBER AND 40H) = 0)                                       AND (NOT CHRRDY) AND (NOT M                                         1188 3         CALL CALC;                                                     1189 3         CALL UPDATE;                                                   1190 4         IF ((CHAMBER AND 20H) ( ) 20H)                                                THEN DO;                                                       1192 4           P15 = 1;                                                     1193 4           SECONDS = 0;                                                 1194 4           TENTHSEC = 0;                                                1195 4           I = 0;                                                       1196 4           HFLAG = 0;                                                   1197 4           LED = 14H;                                                   1198 4           OPERATE = 0AAH;                                              1199 4           TSTART, TEND = 0;                                            1200 4           ACON, AF = SEGMENT (0).SA;                                   1201 4           BCON, BF = SEGMENT (0).SB;                                   1202 4           CALL CHECKMEM;                                               1203 4           END;                                                         1204 3         END;                                                           1205 3      IF (CHRRDY OR MSG) THEN DO;                                       1207 3         IF CHRRDY THEN DUM=KEYBD;                                      1209 3         ELSE DUM = SERRPLY;                                            1210 4         IF NOT HFLAG THEN DO;                                          1212 5           IF DUM = HOLD THEN DO;                                       1214 5             LED = 94H                                                  1215 5             CALL UPDATE;                                               1216 5             HGLAF = 1;                                                 1217 5             OPERATE = 0ACH;                                            1218 5             CALL CHECKMEM;                                             1219 5             END;                                                       1220 5           ELSE IF DUM = STOP THEN DO;                                  1222 5             BEEP.sub.-- CON = 36H;                                     1223 5             ACON = 100;                                                1224 5             BCON = 0;                                                  1225 5             RETURN;                                                    1226 5             END;                                                       1227 4           ELSE IF (DUM ( ) NUL) THEN CALL                                           BADKEY;                                                          1229 4           END;                                                         1230 4         ELSE IF (DUM = RUN) OR (DUM = HOLD)                                      THEN DO;                                                            1232 5           IF MFLAG THEN DO;                                            1234 5             SECONDS = 0;                                               1235 5             P15 = 1;                                                   1236 5             I = 0;                                                     1237 5             TSTART, TEND = 0;                                          1238 5             ACON, AF = SEGMENT (0).SA;                                 1239 5             BCON, BF = SEGMENT (0).SB;                                 1240 5             END;                                                       1241 4           HFLAG = 0;                                                   1242 4           TENTHSEC = 0;                                                1243 4           LED = 14H;                                                   1244 4           CALL UPDATE;                                                 1245 4           OPERATE = 0AAH;                                              1246 4           CALL CHECKMEM;                                               1247 4           END;                                                         1248 4         ELSE IF DUM = STOP THEN DO;                                    1250 4           BEEP.sub.-- CON = 36H;                                       1251 4           OPERATE = 0;                                                 1252 4           ACON = 100;                                                  1253 4           BCON = 0;                                                    1254 4           RETURN;                                                      1255 4           END;                                                         1256 3         ELSE IF (DUM ( ) 0) THEN CALL                                                 BADKEY;                                                        1258 3         GOTO TAG1;                                                     1259 3         END;                                                           1260 2      IF XFILL THEN XFILL = 0;                                          1262 2      ELSE CALL FILL;                                                   1263 2      CALL PUMP;                                                        1264 3      IF (FILLTIME ( 30) THEN DO;                                       1266 3         FILLTIME = 0;                                                  1267 3         CALL FILL;                                                     1268 3         P13, P35 = 1;                                                  1269 3         XFILL = 1;                                                     1270 3         END;                                                           1271 3      ELSE DO J = 1 TO 20;                                              1272 3         FILLTIME = 0;                                                  1273 3         CALL TIME (OFFH);                                              1274 3         END;                                                           1275 2      CALL UPDATE;                                                      1276 2      GOTO TAG1;                                                        1277 1     END RUN.sub.-- MOD;                                                1278 1     START: DISABLE;                                                    1279 1      TACH.sub.-- CON-10110000B;                                        1280 1      TMOD - 100110B;                                                   1281 2      IF (CHAMBER AND 4) ( ) 4 THEN DO;                                          /* 19.2 KBAUD */                                                     1283 2           TH1 = OHDH;                                                  1284 2           PCON = 80H;                                                  1285 2           END;                                                         1286 2      ELSE DO;                                                                   /* 1200 BAUD */                                                      1287 2           TH1 = 0E8H;                                                  1288 2           PCON = 0;                                                    1289 2           END;                                                         ______________________________________                                    

In FIG. 22, there is shown a fragmentary, elevational view, partlybroken away in section of the mixer, degasser and accumulator 46, havinga mixing chamber 823 within a column of porous frit, an influent inlet820, and effluent outlet 822, a reference thermistor 102 and a levelthermistor 100.

The mixing chamber 823 has a volume greater than that of the highpressure pumps cylinder so that the high pressure pump may receive fluidfrom conduct 822 on a fill stroke sufficient to fill its chamber. Thevolume of the accumulator 46 available to hold liquid should be smallenough to permit a new mixture to change the ratio resident in it asrapidly as possible and maintain in it after filling the chamber of thehigh-pressure pump at least one percent of its full volume of liquid. Itmust be large enough for degassing. Its actual volumetric capacity isdetermined by the pump with which it cooperates and is generally between0.25 ml and 500 ml.

The column of frit is hollow to form the mixing chamber 823 and receivesfluid from the inlet 820 into its interior between the inlet 820 andoutlet 822 so that the influent must flow through the frit which servesas a tortuous path and flow spreader before reaching the outlet. Thefluid is injected into the hollow interior of the frit where it is mixedby the momentum of its insertion mass and velocity and then flowsthrough the small pores of the frit to cause further mixing and removalof gases. The surfaces of the frit are of a material and area to causenucleation, and in one embodiment are stainless steel with a pore sizeof 20 micrometers.

The frit should be spaced from the walls of the mixer enough so thateven with the largest flow rate, they have time and space to form on thefrit, to be removed from the frit by solvent flow, and float to the top821 of the mixer for removal through a vent 825 rather than beingcarried to the outlet for the solvent. The outlet is lower than the ventand below the surface of this solvent. With this arrangement, no heliumgas sparging the solvent supply is necessary. The spacing from the wallsmust be at least 0.25 millimeter.

In the preferred embodiment, the frit is cup shaped resting on thebottom by a small cylindrical area. There is substantially no frit orother material besides liquid between the frit, the side walls and thetop. The frit must have pores of a size between 2 and 20 microns indiameter.

The outlet of the mixer may be connected to any type of pump havingsuitable displacement volume. Thus, it may accommodate different makes,pressures, speeds of pumping and the like.

The reference thermistor 102 is mounted adjacent to the bottom of themixing chamber 823 so that as long as there is fluid in the mixingchamber 823, it be covered and will retain heat whereas the levelthermistor 100 will be uncovered upon emptying of the mixing chamber 823and covered when it is filled. Liquid is pumped into the chamber by thelow pressure pump where it degasses against the frit.

In summary, the gradient is programmed within the system controller 22in a digital format and the high pressure pumping system 14 is primed.After priming, the high pressure pumping system pumps at its preset flowrate, emptying the mixer, degasser and accumulator 46 (FIG. 2). When themixer, degasser and accumulator 46 is filled, it sends a signal to theanalog control circuit 40 (FIG. 2) which causes the low pressure pump,valve and motor assembly 42 (FIG. 2) to refill the mixer by filling thepump with the programmed gradient in use at that time and pumping itinto the mixer.

To program the gradient, up to nine segments each relating to adifferent mixture of solvents may be keyed into the keyboard 52 (FIG. 2)to establish a digital representation of the up to nine solvent mixturesto be used across the time of the chromatographic run. The flow rate mayalso be introduced.

In the embodiment of FIGS. 17-21, the time of the chromatographic runand the shape of the segments may be set by selecting the: (1)particular outputs of counter 742 (FIG. 18) to select the time up toreset; (2) by selecting particular outputs of the counter 742 to movefrom segment (such as 740A or 740B) within the switches (such as 754 Aor 754B) to select the segment; and (3) setting within segments by theswitches within the time of run and segment selector 766 (FIG. 19),valve opening times for the valves containing solvents to introducesolvent into the pump chamber as the pump is filling and thus controlthe proportions of mixtures.

To prime the high pressure pump, a signal is continuously applied fromthe keyboard to valves 70 and 72 causing fluid to flow into the pump 62during each cycle and the demand signal is continuously applied to thelow pressure pump to cause continuous pumping until pumping is observedfrom the high pressure pump, after which time, the signals are manuallyreleased. The flow rate may be set in a conventional manner and is notpart of this invention, the setting being applied directly to the highpressure pump.

To provide a proper mixture of solvents to the mixer, degasser andaccumulator 46 (FIGS. 2, 3 and 22), the sensing circuit 92 senses whenthe liquid in the mixer, degasser and accumulator 46 drops below one oftwo thermistors indicating an empty condition and transmits signals tothe unbalance signal and first derivative circuit 94, and logic whichgenerates a signal to an output logic circuit and to a second derivativecircuit 98 which initiates a pumping and valve command to obtain moresolvent in the mixer. The signals are compensated by the temperaturecompensation circuit 90 connected to the unbalance signal and firstderivative circuit 94.

When an empty signal is sensed by the ANDing of the first and secondderivatives or the unbalance signal between thermistors alone, thesignals are applied to a logic circuit which begins a refill cycle.During the refill cycle, the programmed gradient is incorporated intothe pump during the fill portion of the pump 62 as the pump is drawnback.

During the fill stroke, a valve port to one of the solvents is open toenable fluid to flow into the pump cylinder while the pump is operatedat medium rate sufficiently slow to avoid cavitation. It is slowedfurther after the system controller 22 indicates that an amount lessthan the proper amount has been introduced. The first valve closes itsfirst part and opens its second while the pump is moving slowly. Whenthe valve opening is sensed, the pump speed is increased as soon as thevalve transition is sensed by a circuit indicating it is opening. It isslowed after the system controller 22 indicates somewhat less than theproper amount of that solvent has been introduced.

As the first valve closes, the pump speed is slowed and when closed, avalve to the second solvent is opened while the pump is moving slowly.When the valve is fully opened, it is sensed and a signal applied toincrease the return pump speed until the programmed amount of the secondsolvent has been introduced.

This process can be repeated for a third solvent in the preferredembodiment but with minor modifications any number of solvents may beemployed.

Once the pump has been filled with the proper mixture of solvents, theforward stroke begins to introduce the solvent at a high rate to rapidlyintroduce the solvent into the mixer, degasser and accumulator 46 sothat proper mixing takes place from the hydrodysiosis forces.

In the operation of the valves, there is a delay between when the valveis snergized and the plunger begins to move. In general, this time isnot reliably constant. The system controller stores the time betweenwhen the valve is energized and the plunger begins to move. This time isstored and used to correct the lead time between energization and thevalve port switching time for the next valve switching cycle, so thatthe plunger moves at the proper time to insure accuracy in solventcomposition.

In the preferred embodiment, the valves are 3-way solenoid 161K031Avalves manufactured and sold by Neptune Research, Inc., having officesat 481 Gleasondale Road, Stow, Mass. 01775, with all orifices bored to40 thousandths diameter to prevent unfavorable pressure drops.

As can be understood from the above description, the chromatographicsystem 10 of this invention has several advantages: (1) the mixingefficiency of the system is independent of the flow rate of the highpressure pump that is supplied with solvents by the gradient programmer;(2) the gradient programmer is able to prime the high pressure pump; (3)the gradient programmer is able to mix several solvents with precisioneven though some of the solvents may be a low proportion of the mixture;(4) it is economical; and (5) it degasses the mixed solvent.

Although a preferred embodiment of the invention has been described insome detail, many modifications and variations are possible in thepreferred embodiment without deviating from the invention. Accordingly,it is to be understood, that, within the scope of the appended claims,the invention may be practiced other than as specifically described.

We claim:
 1. A mixer for a liquid chromatograph comprising:achromatography column; a first pump; a second pump; means foraccumulating liquid; means for receiving liquid from a first pump; meansfor making the accumulated liquid available to a second pump; a porouswalled fluid barrier comprising a frit; said porous-walled fluid barrierbeing positioned between said means for receiving liquid and said meansfor providing liquid whereby said liquid passes through said porousmaterial after being received from said inlet and before being madeavailable at said outlet; said porous material being capable of causingnucleation of gasses to degas said liquid; and level measuring means forproviding a signal when liquid in said mixer falls between apredetermined level.
 2. A mixer according to claim 1 in which said frithas pores of a size between 2 and 20 microns in diameter.
 3. A mixeraccording to claim 2 in which the volume of said mixer is between 0.25ml and 500 ml.